Flow Measurement in the Vascular Access Conduit: an Ex Vivo Experimental Model

ABSTRACT

PURPOSE: Previously, we developed a new method to calculate the flow rate in the hemodialysis vascular conduit based on Bernoulli's theory for surveillance of the arteriovenous fistula (AVF) function. However, the calculated flow rate would be different from the true flow rate because due to various factors. To compare the true flow rate, with intra- conduit pressure, and the calculated flow rate, an ex vivo experimental model was developed. METHODS: The arterial end of the vascular conduit was connected to a saline-filled bottle, with the venous end connected to a flow meter to control the flow rate. By monitoring the change in the true flow rate (Q) with the flow meter, each arterial and venous static pressure (pA, pV) and total pressure (pT) were observed. Using these parameters, the intra-conduit flow rates (QA, QV) were calculated by Bernoulli's equation. Finally, we compared the pA or pV with Q, and calculated the difference between the QA or QV and Q. RESULTS: There were no statistical differences between any of the pressure measurement during the 5 consecutive 5 experiments (P<0.05). The static pressure (pA or pV) was closely correlated with Q (pA, R2=0.950, P=0.000; pV, R2= 0.952, P=0.000). The calculated flow rate (QA or QV) was not in complete in accord with Q, but was closely correlated (QA, R2=0.961, P=0.000; QV, R2=0.961, P=0.000). CONCLUSION: The pressure measurement and calculated flow rate indicate the nature of the true flow rate in the vascular conduit.